Image display systems based on spatial light modulators (SLMs) are increasingly being used as an alternative to image display systems based on cathode ray tubes. As used for image display applications, SLMs are arrays of pixel-generating elements that emit or reflect light to an image plane. The pixel-generating elements are often themselves referred to as "pixels", as distinguished from pixels of the image. This terminology is clear from context, so long as it is understood that more than one pixel of the SLM array can be used to generate a pixel of the image.
The pixels of the SLM are individually addressable, such that the image is defined by which pixels are on or off at a given time. Moving images can be generated by re-addressing the SLM with data for successive frames. Greyscale images can be created with various modulation schemes, and color images can be created by filtering the emitted or reflected light.
For addressing the pixels of the SLM, each pixel is in communication with a memory cell that stores a bit of data that determines the on or off state of an address signal. The addressing is binary in the sense that each pixel is addressed with a high or low signal that indicates whether or not the pixel is to emit or reflect light to the image plane. The SLM is "loaded" by storing data in the memory cells, via a data loading circuit peripheral to the SLM's array of pixels.
The memory cells of the SLM are loaded with data that has a special "bit-plane" format. This format permits greyscale images to be generated by addressing each pixel with successive address signals during a frame period, each address signal representing a different bit weight of that pixel's n-bit pixel value. For example, for 8-bit pixel values (256 levels of intensity), each pixel is represented with eight bits of data, and addressed eight times during a frame. Each time the pixel is addressed, the bit value determines whether the pixel is on or off and the bit weight determines how long the mirror remains on or off. The human eye integrates light from the on and off times and sees a greyscale image.
Various schemes for converting data from pixel format to bit-plane format for SLMs are described in U.S. Pat. No. 5,255,100, entitled "Data Formatting with Orthogonal Input/Output and Spatial Reordering", and in U.S. Pat. No. 5,278,652, entitled "DMD Architecture and Timing for Use in a Pulse Width Modulated Display System". In the past, such formatting schemes have required some form of double buffering to maintain a continuous stream of data. Data in pixel format is written into one array of memory cells while bit-plane data is read from a second array.